If PKCS1 parsing of the SSH key fails, try PKCS8
If no image is generated, just return nil for the Openstack provider

This mirrors what is done in other providers e.g. Amazon providers
Merge pull request #375 from justinsb/avoid_nil_pointer_if_no_openstack_image

builder/openstack: If no image is generated, just return nil
Update CHANGELOG
Merge pull request #376 from justinsb/try_parse_pkcs8

communicator/ssh: If PKCS1 parsing of the SSH key fails, try PKCS8
Update CHANGELOG
website: page titles on provisioner docs
website: fix typo s/script/shell/ provisioner
builder/openstack: don't hardcode "DFW" and make region required
website: document required openstack region setting
website: fixup some underscores to not be emphasis in the AWS docs
website: add openstack to the intro platforms list
builder/openstack: region is now required